DL-LACTONE

Animals NMRI BR (SPF) mice from Charles River, Sulzfeld, Germany were used. Animals were young adults (6-8 weeks old), females were nulliparous and non-pregnant. The animals were housed in an air-conditioned room with approximately 15 air changes per hour, a temperature of 22±3 °C and a relative humidity between 30 and 70%; inspite of the relative humidity exceeding 70% for part of the test period, no abnormalities were noted in the animals and it was concluded that this deviation did not affect the integrity of the study. The animal room was illuminated for 12 hours per day with artificial fluorescent lighting and was dark for 12 hours. The animals were housed in randomised groups of 5 each per sex per cage in labelled polycarbonate cages containing purified sawdust (Sawi, Jelu-Werk, Rosenberg, Germany) as bedding material. Paper bedding (BMI Helmond, The Netherlands) was provided for nest material. There was free access to standard pelleted diet (Altromin (code VRF 1), Lage, Germany) and to tap water. Certificates of analysis for all substrates, feed and water are retained in the NOTOX archives. For all animals there was an acclimatisation period of at least 5 days before start of treatment under laboratory conditions. Treatment groups Two dose groups, one of 4 males and 4 females at 2000 mg/kg bw and one of 3 males and 3 females at 1500 mg/kg bw, all administered by gavage in 10 ml of physiological saline, were used for the dose range-finding test. 5 males each per test group respectively were used as negative and positive controls as there were no obvious differences between sexes in the range-finding test. All animals were identifed by a unique number on the tail. In the main test there were 6 groups of 5 male and 5 female mice each, labelled A through F. A was a negative control (vehicle only, 10 ml physiological saline/kg bw) group, B and C were high-dose treatment groups (1500 mg dl-lactone/kg bw in physiological saline, dose adjusted to a volume of 10 ml/kg bw; group B to be sampled at 24 hours post-dosing, group C at 48 hours post-dosing); D and E were middle- and low-dose treatment groups (D 750 mg and E 375 mg dl-lactone/kg bw in physiological saline, both groups D and E to be sampled at 24 hours post-dosing), while F was the positive control group (50 mg cyclophosphamide/kg bw, dissolved in physiological saline, sampling at 48 hours; cyclophosphamide from Asta-Werke, Germany). Feed was withheld 3-4 hours prior to dosing. Administration was by oral gastric intubation. Observations The animals were observed at least once a day for signs of toxicity. Prior to dosing the animals were weighed. Preparation of erythroblasts and erythrocytes